Water colours

Photo by Rusty Clark

In late summer, quiet bays and river oxbows are ablaze with purple blooms. The Ojibway called it “the pike’s plant,” but English settlers – who often used the term “pike” and “pickerel” interchangeable – called it pickerelweed.

Pickerelweed grows in quiet bays and oxbows just about everywhere east of the Rockies. And it is, indeed, a great place to find pike. The big, toothy predators are ambush hunters, and love to spend their days lurking amid thick forests of stems, waiting for a sunfish or a frog to saunter past. With a thrust of its powerful tail, the pike will burst forward and snatch a meal, then retreat to the gloomy waters to digest. Pickerelweed, which grows in dense stands, makes an ideal ambush location.

Those dense stands serve another important function, providing a solid mass of roots and stalks that stabilize shorelines. If you have pickerelweed growing along the shore, you’re unlikely to have much of an erosion problem.

What makes pickerelweed unusual is how much one plant will vary from another, particularly when it comes to leaf shape. In most plant species, the leaves don’t vary much – one sugar maple leaf may be larger or smaller than another, but the shape is pretty consistent. That is, after all, one of the key ways to tell a sugar maple from a red maple, or a striped maple, or any of dozens of other maples.

But pickerelweed leaves are all over the place. They’re generally shaped like a heart or an arrowhead, but some are sharp and spear-like while others are almost egg-shaped. Even within an individual plant, the leaf shape can vary.

There’s another plant called arrowhead that grows in very similar conditions to pickerelweed, and also has arrow-shaped leaves. Without the flower stems, it can be tricky to tell the two plants apart.

Arrowhead blooms are white, but from late June to fall, pickerelweed can be easily identified by its tall stems of purple flowers. Each bloom lasts just one day, so over the course of the season the stems gradually become filled with seeds. As the seeds mature, they drop into the water. Most of them become food for muskrats or ducks, but a few drift downstream and slowly settle into the muck to form a new colony of pickerelweed.

Most of the plants growing in a patch didn’t grow from seed, though: pickerelweed sends roots out in all directions, which produce new shoots. What looks like multiple plants is, in fact, usually a mass of clones all sprung from the same parent plant.

That ability to spread has made pickerelweed an invasive nuisance in Europe and Africa, where the plant isn’t native. Introduced to ornamental water gardens, it has spread into the wild in South Africa, Tanzania, England, and other countries, where there are efforts to eradicate it. In South Africa, gardeners are encouraged to plant a more sustainable native like calla lily; in parts of North America and throughout Australia, calla lily is cited as an invasive plant, which goes to show that a weed really is just a plant that’s growing somewhere you don’t want it to grow.